Polygonal cutting insert

ABSTRACT

A polygonal cutting insert with at least one rib-shaped raised elongated cutting component of the face arranged at a distance from the cutting edge and extending generally in the chip removal direction. The rib has a front end spaced inwardly of the cutting edge and a cross section increasing from the front end to a region at which the cross section is a maximum and then decreasing from that maximum to a rear end of the rib.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/DE 95/01119 filed Aug. 19,1995 and based, in turn, on German National Application P 44 37 093.8 ofOct. 17, 1994 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a polygonal cutting insert with at least oneraised longitudinal rib-shaped cutting element arranged on the face ofthe insert at a distance from the cutting edge and extendinglongitudinally to define a longitudinal axis. The elongated cutting ribis arranged substantially in the chip removal direction, whereby thelongitudinal rib section, seen in the direction of chip removal, has amaximum.

BACKGROUND OF THE INVENTION

Such a cutting insert is described for instance in DE 42 39 236 A1. Thelongitudinal ribs described therein have in there longitudinal section aminimum and a maximum in a region away from the cutting edge, or are atthe same level as a central face plateau raised with respect to thecutting edges or corners. Seen in cross section, the longitudinal ribscan have a constant width over their entire longitudinal axis or canbecome wider towards a region located at a distance from the cuttingedge. In the case of relatively large initial curvature radii of theremoved chip, particularly when the cutting element is used with smalladvance, these ribs make it possible to bend up the chip as much aspossible. In the case of high advance rates, due to the maximum orgreatest height located at a distance from the cutting edge it ispossible to act counteract a very small initial curvature radius, i.e. avery tight curling of the chip.

A cutting insert having longitudinal ribs with a parabolic crosssection, arranged along the cutting edge at identical acute angles, isdescribed in DE 41 18 070 A1. Cutting inserts with longitudinal ribshaving at least one recess reaching up to the cutting face, aredescribed in the WO 92/21467. Finally there are also known cuttinginserts with raised cutting elements or a median raised face plateauwhich has nose-like or wedge-like projections pointing in the directionof the cutting corner or cutting edge.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a cutting insertsuitable for turning, lancing, milling and like machining operations,particularly for steel and for materials with relatively difficult chipcontrol, such as highly alloyed steel and titanium-aluminum alloys,whose face geometry forms the removed chip during cutting in the regionimmediately adjacent to the cutting edge, without allowing the removedchips to put undue strain on the cutting insert itself.

Another object of the invention is to provide an improved cutting insertwhich has wear-resistant ribs, capable of withstanding even the strongfriction, resulting from roughing-down operations or due to the type ofmaterial machined.

SUMMARY OF THE INVENTION

These objects are achieved by a cutting insert wherein, according to theinvention, a the longitudinal rib has a ascending slope or inclinedflank facing the cutting edge and which widens towards a region spacedaway from the cutting edge and reaches its greatest width in the regionof the maximum cross section of the rib. The longitudinal rib has anupper surface or flank descending and narrowing from the region of themaximum to a region further away from the cutting edge and the region ofthe maximum projects above the cutting edge.

This cutting insert can insure that the chip is bent away from the faceof the cutting insert immediately behind the cutting edge by theascending slope, whereby the cutting insert is noticeably relieved afterthe chip slides away over the maximum of the longitudinal rib. Thedescribed longitudinal rib offers optimal chip guidance counteracts thelateral deflection of the chip. Besides the friction of the chip againstthe face is kept as low as possible.

The longitudinal rib can have longitudinal axis which is set at an anglebetween 30° and 150°, preferably between 60° and 120°, with respect tothe cutting edge. The layout of the longitudinal rib or ribs, whichpreferably are parallel to each other, is essentially determined by thechip removal conditions and the chip flow.

In order to provide a noticeable relief from the friction with theremoved chip at the descending upper surface, each of the lateral edgesforming the junction of the descending upper surface with the adjacentlateral flanks of the longitudinal rib is inclined at an angle between3° and 20°, preferably 5° to 15°, with respect to the longitudinal axisof the longitudinal rib, thereby forming the mentioned narrowing of theupper surface. The respective angles are measured in a plan view of thelongitudinal rib. Preferably the bilateral edges, which laterallydelimit the upper surface, are arranged symmetrically as mirror imageswith respect to the longitudinal axis, i.e. under absolutely equalangles, but with opposite inclinations to the longitudinal axis.Depending on the intended use, they can also be arranged asymmetrically.

The initial width of the ascending slope or front flank at the frontalbase point of the longitudinal rib, which is the point closest to thecutting edge, ranges between 0 and 0.5 mm, preferably 0.2 to 0.3 mm.This width increases to a width which in the region of the maximum,ranging between 0.3 and 1.5 mm, preferably 2 to 4 times the initialwidth.

In order to insure that the chip is seized by the ascending slope almostimmediately after its formation at the cutting edge, the distance of thelongitudinal rib from the cutting edge is 0.03 mm to 1 mm, preferably0.05 mm to 0.3 mm. The total length of the longitudinal rib whichcomprises the length of the ascending slope and of the descending uppersurface ranges between 1.0 mm and 8 mm, preferably 1.5 mm to 4 mm,whereby the length of the ascending slope lies between 0.3 mm and 1.5mm, preferably between 0.4 and 0.8 mm. The front flank thus is clearlyshorter than the descending upper surface. The ascending slope issubstantially flat and has an angle of ascent of between 10° and 45°,preferably 20° to 30° with respect to the face adjacent to the cuttingedge. As an alternative it is also possible to shape the ascending slopeconcavely or convexly seen in the direction of the longitudinal axis,whereby the tangential surfaces in the median area of the ascendingslope have angles of ascent of the aforementioned magnitude with respectto the face adjacent to the cutting edge. The maximum can be sharp-edgedor convex seen in the direction of the longitudinal axis. If the regionof the maximum is curved a radius between 0.1 mm and 1 mm, preferablybetween 0.25 mm and 0.5 mm, is preferred.

The descending and narrowing upper surface has in the direction of thelongitudinal axis an angle of inclination between 5° and 40°, preferably5° and 25°, with respect to the face bordering on the cutting edge.Preferably an inclination angle is selected which is equal to theeffective cutting angle, i.e. the angle between the face and atheoretical perpendicular to the machining surface. The longitudinalribs can have convex or concave upper surfaces.

As has already previously been mentioned, it is possible to arrangeseveral longitudinal ribs in the region with an interspacing between twoneighboring maxima which is 1.5 to 5 times, preferably 1.5 to 3 timesgreater than the width of the respective maxima (measured transverselyto the longitudinal axis of the longitudinal rib).

The cutting insert has longitudinal ribs with lateral flanks borderingthe ascending slope and/or the upper surface, which seen transversely tothe longitudinal axis, can be concave, convex or essentially flat.Particularly in the area bordering the face surrounding the longitudinalrib or in the area of the ascending slope and/or at the upper surfaceedge roundings can be provided. The lateral flanks have inclinationangles with respect to the face surrounding the longitudinal ribs or thecutting edge plane ranging between 15° and 45°, preferably between 20°and 35°. These inclination angles are defined by the connection linebetween the base point of the lateral flank on the face and the limitpoint to the ascending slope or the upper surface. Seen in transversedirection to the longitudinal axis, the ascending slope and/or the uppersurface run parallel to the cutting edge or at a positive or negativeangle up to 15°.

The surface of the insert adjacent the cutting edge can be provided witha chamfer adjacent to the cutting edge, which is at a positive ornegative angle. Depending on the chamfer width, the ascending slope canreach into the region of the chamfer.

According to the invention, the maxima of the longitudinal ribs arealways above the level of the cutting edge, in the working position ofthe cutting insert during machining, as well as in the flat position ofthe cutting insert. The height by which the maximum lies above thecutting edge at the intersection point between the extended longitudinalaxis and the cutting edge ranges between 0.05 mm and 0.5 mm, preferably0.1 mm and 0.3 mm.

According to a further embodiment of the invention, several longitudinalribs can be arranged along the cutting edge, at various angles ofinclination, of various size, shape and height within theabove-described limits.

Preferably the cutting insert has a positive free flank. The cuttingedge can be straight, convex, concave or sinuous.

According to a further embodiment of the invention, in addition to thedescribed longitudinal ribs, further raised cutting elements or cuttingrecesses or cutting grooves or notches can be provided. In this respectreference is made particularly to DE 41 41 368 A1, DE 41 18 065 A1 andDE 41 36 417 A1. The basic shape of the cutting insert can be rhombic,square, triangular or round, whereby the cutting insert can be one-sidedwith cutting elements provided on a single side of the cutting surfaceor it can be a two-sided cutting insert with opposite faces with cuttingelements. Optionally the cutting element to be used only on one side canbe designed to have a protection chamfer against chip impact.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1a is a top view of a rhombic cutting insert according to thepresent invention.

FIG. 1b is a fragmentary plan view of the cutting insert of FIG. 1during workpiece machining,

FIG. 2 is a perspective view of a portion of the cutting insert of theinvention with a negative chamfer;

FIG. 3 is a fragmentary top view of a cutting insert showing thedimensions of a longitudinal rib;

FIGS. 4a and 4b are respective sectional views taken along lines A--Aand B--B of FIG. 1a

FIGS. 5a, 5b, 5c and 5d are sectional views along a line C--C of FIG. 1ashowing various embodiments;

FIGS. 6a, 6b, 6c, 6d and 6e are further sectional views along line A--Aof FIG. 1a showing various embodiments;

FIGS. 7a and 7b are detail frontal views of cutting inserts of theinvention in various embodiments;

FIGS. 8a, 8b and 8c are front views of other cutting edge shapes;

FIGS. 9a, 9b and 9c are side views of various cutting inserts accordingto the present invention;

FIG. 10 is a fragmentary top view of a cutting insert with thelongitudinal ribs of the invention and further cutting elements.

SPECIFIC DESCRIPTION

In FIG. 1a a top view of a rhombic cutting element 10 is shown, whichhas four cutting corners 11, each continued by the respective cuttingedges 12. Along the cutting edge 12 which continue the cutting corner 11used during cutting, several mutually parallel longitudinal ribs 13 canbe seen, each having a longitudinal axis 14 set at identical angles. Inthe present case four longitudinal ribs 13 are illustrated, which arearranged in the region of the maximal cutting depth in the workpiece 32(see FIG. 1b). The face segments adjacent to the other cutting cornersalong the respective cutting edges have corresponding longitudinal ribs(not shown). The number of the longitudinal ribs arranged on the face isnot limited, but at least one longitudinal rib is provided.

As shown in FIG. 1a, the cutting insert can have a median face plateau15 which is raised the cutting edge plane. Further the cutting inserthas a central mounting hole 16 through which a tightening screw canpass. Alternately it is also possible to provide clamping projections,fastening depressions or the like fastening elements arranged ascentrally as possible, which in conjunction with a correspondinglyshaped clamping finger make it possible to securely fasten of thecutting insert to the tool holder.

The respective longitudinal ribs laid out along the cutting edge canvary in their shape, size, direction, number and combination with othercutting elements known to the state of the art, as will be explained forinstance with reference to the cutting insert of FIG. 10.

The ribs should be uniformly oriented in the direction of the chipremoval, i.e. the chip removal direction should determine the directionof the longitudinal axis 13 of the cutting elements. The longitudinalribs 14 are relatively close to the cutting edge 12 with their frontaledge, so that they can act almost immediately on the removed chip aftercutting. The highest rib points created by the maximum to be laterexplained are always located above the level of the cutting edge 12, inthe position of use when the cutting insert is fixed in a tool holderand directed at the workpiece to be cut at a cutting angle determined bythe nature of the material, as well as in a position wherein the cuttinginsert is laid on a flat horizontal plane.

The longitudinal ribs of the invention are uniform with an ascendingslope or front flank 20 facing the cutting edge 12 and which widenstowards a region spaced away from the cutting edge. The ascending slopeends in a maximum, followed by a descending upper surface 22 whichnarrows towards a region further remote from the cutting edge. Theascending slope and the upper surface are each defined by border lines,having lateral flanks on each side. Generally the ascending slope, seenin the direction of chip removal, has to be considerably shorter thanthe descending upper surface. The ascending slope, as well as thedescending upper surface, are shaped like wedges, whereby the ascendingslope has absolutely a greater angle of ascent then the inclinationangle of the upper surface.

As shown in FIGS. 1a, 1b and 2, a chamfer 17 adjoining the cutting edge12 can be provided, which runs at a 0° angle or at a positive ornegative angle. FIG. 2 shows an embodiment with a negative chamfer 17.Adjoining the cutting edge 12 is a free flank 18, which is arranged at alead angle of 0° or a positive lead angle. The face 19 adjoining thecutting edge 12 or a chamfer 17 can be designed to descend towards theareas away from the cutting edge or shaped like a depression, as can beseen in the perspective view of FIG. 2. The longitudinal ribs 13 areessentially located in this depression, but the ascending slope 20 risesat least partially above a possible chamfer 17.

As can be seen especially from FIGS. 2 to 4a, 4b, the longitudinal ribshave a distance a₁ from the cutting edge 12, which equals at least 0.03mm, preferably 0.05 mm to 0.3 mm. In its frontal region facing thecutting edge 12, the longitudinal rib 13 can start out with a point orwith a width b1, i.e. the width b₁ shown in FIG. 3 equals 0 mm to 0.5mm, preferably 0.2 mm to 0.3 mm. The ascending slope 20 widenscontinuously towards the cross-sectional area maximum of the rib fromthe cutting edge to a width b₂ which ranges between 0.3 mm and 1.5 mm,whereby in the case of a predetermined positive width b₁, the width b2is 2 to 4 times greater than the width b₁. The ascending slope ends inan edge 21, which also represents the maximal height of the longitudinalrib. In the following this edge 21 is also referred to as the maximum21. The surface 22 extends from edge 21 toward a region more remote fromthe cutting edge, the edge 21 running transversely with respect to thelongitudinal axis 14 of the longitudinal rib 13. This descending uppersurface 22 narrows rearwards. The narrowing is determined by the anglesα₁ and α₂, which range between 3° and 20°, preferably 5° to 15°. Theseangles α₁ and α₂ are formed by the lateral edges 23 and 24 of the uppersurface with respect to the direction of the longitudinal axis 14. Theangles α₁ and α₂ can be equal or different, whereby the upper surface ismirror-image symmetrical or also asymmetrical with respect to thelongitudinal axis. The total length a₂ of the longitudinal rib liesbetween 1 mm and 8 mm, preferably 1.5 mm to 4 mm. The length a₃ of theascending slope 20 is between 0.3 mm and 1.5 mm, and the length of theupper surface 22 is clearly greater than the length a₃ of the ascendingslope 20. For instance the value a₂ -a₃ can be more than 5 times greaterthan a₃. On the sides of the ascending slope 20 the longitudinal rib haslateral flanks 25, each forming a common edge 26 with the ascendingslope 20. The edge 26 forms with the longitudinal axis 14 an angle α₃,which here has approximately 30°. This angle is determined by therespective width b₁ and b₂, as well as by the length a₃ of the ascendingslope. The edges 23 and 24 are adjoined laterally by the lateral flanks27, whose width according to the construction (see top view according toFIG. 3) decreases to 0 in the areas away from the cutting edge, sincethe upper surface has a more noticeable descent in the areas away fromthe cutting edge than the face surrounding the longitudinal ribs. In thepresent case the upper surface 22 merges into the face at 28. Theangular setting of the lower edges 29 and 30 of the lateral flanks 25and 27 is determined by the flank angles γ₁ and γ₂ corresponding to FIG.5a, which range between 15° and 45°, preferably 20° to 35°. The anglesγ₁ and γ₂ can be identical or different. The longitudinal axis 14 formswith the cutting edge 12 an angle α₄, which ranges between 30° and 120°,preferably between 60° and 120°. The angle of the longitudinal axis 14is determined essentially by the chip removal direction 31 (see FIG.1b).

As can be seen in FIGS. 1a, b and FIG. 2, if there are severallongitudinal ribs, preferably arranged parallel to each other along thecutting edge 12, then the distance between them equals b3, which ismeasured between respectively neighboring end points of the respectivemaximum 21. This distance is 1.5 to 5 times, preferably up to 3 timesgreater than the aforedescribed value b2.

The ascending slope 20 reaches at least partially into the area definedby the chamfer 17, preferably in such a manner that the lateral flanks25 adjoining the ascending slope 20 end rearward with the chamfer 17.The longitudinal ribs 13, or their longitudinal axis 14, are arranged ata right angle or an acute angle with respect to the cutting edge.However the extension of the longitudinal axis 14 can also be orientedtowards the apex of the cutting corner 11.

In FIG. 1b a cutting insert is shown in process of the machining aworkpiece 32. The arrow 33 shows the advance direction of the cuttinginsert in relation to the workpiece 32, which is being machined with amaximal cutting depth. In the area of this cutting depth a, along thecutting edge 12 at least one longitudinal rib 13 is provided, whoselongitudinal axis 14 is oriented in the chip removal direction 31, i.e.parallel thereto. The removed chip is formed in the immediate vicinityof the cutting edge by the ascending slope 20, but the cutting insert isnoticeably relieved by the narrowing upper surface 22. force requiredfor deflecting the chip is relatively small, and the longitudinal ribsremain resistant to wear even during roughing-down operations andfriction due to the nature of the material.

The sectional views according to FIGS. 4a and 4b show that thelongitudinal rib profile has a roof-like configuration. The angle β₁ ofthe ascending slope 20 lies between 10° and 45°, preferably between 20°and 30°, while the angle β₂ formed by the upper surface 22 with thecutting edge plane ranges between 5° and 40°, preferably 5° and 15°. Theangle β₂ can be parallel to the effective cutting angle. The end of theascending slope forms the maximum 21, whereby the respective edge canalso be rounded with an edge radius between 0.1 mm and 1 mm, preferably0.25 mm and 0.5 mm. In relation to the cutting edge 12 the maximum 21lies at a distance h₁ between 0.05 mm and 0.5 mm, preferably 0.1 mm and0.3 mm.

FIGS. 5a to 5d show cross sectional views along sections perpendicularto the rib axis in the area of the descending upper surface 22. Howevera corresponding situation is valid for the area of the ascending slope20 and the maximum 21. The upper surface 22 can be flat or also concave(see FIG. 5d) and parallel or also set at positive angles Δ₁ or negativeangles Δ₂. The lateral flanks 27 are flat (FIG. 5a), concave (FIG. 5b)or also convex (FIG. 5c), respectively set at the already describedangles γ₁ and γ₂. In the case of concave or convex flanks theinclination angle γ is defined by the border surface 30 and the upperedge 24, respectively the edges 29 and 26.

FIGS. 6a to 6e show various designs of faces and longitudinal ribprofiles. The face can be designed without a chamfer (FIG. 6a), with a0° chamfer (FIG. 6b) or a negative chamfer (FIG. 6c). In the area of theupper surface 22 the longitudinal rib profile is flat, concave (FIG. 6d)or convex (FIG. 6e), each seen in the direction of longitudinal axis 14.The face surface surrounding the longitudinal ribs 13, optionallyadjoining a chamfer 17, slopes downwardly towards the rear, particularlyby passed into a chip-forming recess 34.

Considered from the cutting corner 11 towards the cutting edge 12, therib height h₁ can increase or decrease or be designed alternatingly, ascan be seen in FIGS. 7a and 7b. In the spirit of the present invention,when on the face of a cutting insert 10 several longitudinal ribs 13 arearranged, all angle sizes α₁ to α₄, β₁, β₂, γ₁, γ₂, Δ₁ and Δ₂, as wellas the length a₁ to a₃ and the widths b₁ and b₂ can be varied within theabove-described limits. The same applies to the distances b₃ between thelongitudinal ribs.

In relation to the corner 11 the cutting edge 12 can have a positiveangle of inclination (FIG. 8a), a negative angle of inclination (FIG.8b) or also a sinuous shape (FIG. 8c). Thereby result correspondingconvex, concave or alternating cutting edge configurations.

When the cutting insert 10 is designed as a one-sided cutting insertcorresponding to FIG. 9, i.e. with only one face 19 opposite to acontact surface 35, the cutting insert can have in addition a protectionchamfer 36 against chip impact in the area bordering on the bottomsurface 25. When a cutting insert is designed for two-sided useaccording to FIG. 9, median plateaus 15 are provided at the upper andlower faces, which surpass the cutting elements, particularly thelongitudinal ribs 13. FIG. 9c shows a cutting insert with a positivefree flank 18.

In the embodiment of the cutting insert according to FIG. 10, the facehas various cutting elements, i.e. in addition to the already describedlongitudinal ribs 13 there are also further cutting elements. In thepresent case in the area of each cutting edge two longitudinal ribs 13are provided, whose longitudinal axes, respectively longitudinal axisextensions intersect with the cutting edge 11 which is tapering off.Longitudinal ribs 37 are provided to either side of the array of ribs 13at each corner. The longitudinal ribs 37 have frontal areas designedcorrespondingly to the aforedescribed longitudinal ribs 13. However inthe areas remote from the cutting edge further projections 38 and 39 areprovided, whereby the projection 38 also represents essentially alongitudinal rib, but differently from the longitudinal ribs of theinvention it has a rounded upper edge. The side facing away from thecutting edge is adjoined by a partially spherical element 39, as anelement lying transversely to the longitudinal axis 40 of the projection38.

The cutting elements 37 to 39 are arranged in a symmetrical mirror-imagefashion in relation to the bisectrix of the cutting corner 41.

In the more remote areas with respect to the cutting edge also a furtherrib-shaped element 42 is provided with an upper surface 43, which runstransversely with respect to the cutting edge plane, and tapers off intothe face area, so that a flank 41 is provided only on one side, i.e. onthe side facing the cutting corner bisectrix 41. This rib 42 to 44represents a modification of the rib 13 of the invention, in that it hasan ascending slope and an upper surface set at such an acute angle thatit serves approximately only as a half rib. In an area more remote withrespect to the cutting edge there is an adjoining parabolic rib 45,which has on both sides partially spherical projections 46.

Further the cutting insert shown in FIG. 10 has a median plateau 15,which in the area of the cutting edge median has projecting parts 47serving for a better support of the plateau when positioned in a toolholder. This cutting insert is designed as an indexable insert withopposite faces.

We claim:
 1. A cutting insert comprising:a polygonal cutting insert bodyformed with at least one cutting corner, a top side, and a front sideadjoining said corner and forming a cutting edge with said top side; andat least one cutting element in the form of an elongated rib formed onsaid top side of said body and having a longitudinal axis extendingsubstantially in a chip-removal direction, said rib having a front endspaced from said cutting edge and a cross section increasing from saidfront end to a region at which said cross section is a maximum anddecreasing from said maximum to a rear end of said rib, said ribhaving:an ascending front flank rising from said front end and wideningtoward a greatest width as said region, a descending upper surfacedirectly adjoining said ascending front flank at said region andnarrowing away therefrom to said rear end, and a height of said regionsuch that said region lies above said cutting edge.
 2. The cuttinginsert defined in claim 1 wherein said longitudinal axis includes anangle (α₄) between 30° and 150° with said cutting edge.
 3. The cuttinginsert defined in claim 1 wherein said rib has a pair of lateral flanksadjoining said upper surface at respective lateral edges of said uppersurface, said lateral edges being inclined to said longitudinal axis atangles (α₁, α₂) between 3° to 20°.
 4. The cutting insert defined inclaim 1 wherein said ascending front flank has an initial width at saidfront end between 0.0 mm and 0.5 mm and increases to said greatest widthwhich is between 0.3 mm to 1.5 mm and 2 to 4 times said initial width.5. The cutting insert defined in claim 1 wherein said front end of ribis spaced between 0.03 mm and 1 mm from the cutting edge.
 6. The cuttinginsert defined in claim 1 wherein said rib has a length between 1.0 mmand 8.0 mm and said ascending front flank has a length between 0.3 mmand 1.5 mm.
 7. The cutting insert defined in claim 1 wherein saidascending front flank is flat and has an angle with said top sideadjacent said cutting edge range between 10° and 45°.
 8. The cuttinginsert defined in claim 1 wherein said ascending front flank is curvedand a tangent to said ascending front flank includes an angle with saidtop side adjacent said cutting edge between 10° and 45°.
 9. The cuttinginsert defined in claim 1 wherein said longitudinal rib is convex insaid region with a radius (R₁) between 0.1 mm and 1 mm.
 10. The cuttinginsert defined in claim 1 wherein said upper surface is curved.
 11. Thecutting insert defined in claim 1 wherein a plurality of said cuttingelements are formed to each side of said corner at a spacing betweensaid ribs measured at said region between 1.5 and 5 times the width atsaid greatest width of said ribs.
 12. The cutting insert defined inclaim 1 wherein said elongated rib has lateral flanks adjoining saidascending front flank and said upper surface with angles of inclinationranging between 15° and 45° relative to respective base lines.
 13. Thecutting insert defined in claim 1 wherein said ascending front flank andsaid upper surface lie parallel to said cutting edge transversely ofsaid axis.
 14. The cutting insert defined in claim 1 wherein saidascending slope and said upper surface include angles of up to 15°transversely of said rib relative to a line parallel to said cuttingedge.
 15. The cutting insert defined in claim 1, further comprising achamfer on said body at said cutting edge, said rib extending into saidchamfer.
 16. The cutting insert defined in claim 1 wherein said regionlies above said cutting edge by a height between 0.05 and 0.5 mm. 17.The cutting insert defined in claim 1 wherein a plurality of saidcutting elements are provided on each side of said corner and theelongated ribs of said elements vary from one another with respect toangular orientation, shape and height.
 18. The cutting insert defined inclaim 1 wherein said front side is perpendicular to said top side. 19.The cutting insert defined in claim 1 wherein said front side forms apositive angle with said top side.
 20. The cutting insert defined inclaim 1 wherein said cutting edge is a straight edge.
 21. The cuttinginsert defined in claim 1, further comprising additional raised cuttingelements on said top side.
 22. The cutting insert defined in claim 1wherein said top side is formed with a recess extending to said cuttingedge.
 23. A cutting insert comprising:a polygonal cutting insert bodyformed with at least one cutting corner, a top side, and a front sideadjoining said corner and forming a cutting edge with said top side; andat least one cutting element in the form of an elongated rib formed onsaid top side of said body and having a longitudinal axis extendingsubstantially in a chip-removal direction, said rib having a front endspaced from said cutting edge and a cross section increasing from saidfront end to a region at which said cross section is a maximum anddecreasing from said maximum to a rear end of said rib, said ribhaving:an ascending front flank rising from said front end and wideningtoward a greatest width as said region, a descending upper surfacedirectly adjoining at said region and narrowing away therefrom to saidrear end, a height of said region such that said region lies above saidcutting edge, and said upper surface includes an angle (β₂) with saidtop side adjacent said cutting edge between 5° and 40°.
 24. The cuttinginsert defined in claim 23 wherein said longitudinal axis includes anangle (α₄) between 60° and 120° with said cutting edge, said rib isformed with lateral flanks adjoining said upper surface in respectivelateral edges, said lateral edges including angles (α₁, α₂) between 5°and 15°, said ascending front flank having an initial width (β1) at saidfront end between 0.2 mm and 0.3 mm, said greatest width being 2 to 4times said initial width, said front end being spaced 0.05 mm to 0.3 mmfrom said cutting edge, said rib having a length (α₂) between 1.4 mm and4 mm, said ascending front flank having a length (α₃) between 0.4 mm and0.8 mm, said ascending front flank forming an angle with said top sideadjacent said cutting edge between 20° and 30°, said angle (β₂) includedbetween said upper surface and said top side being 5° to 15°, saidregion projecting above said cutting edge by 0.1 mm to 0.3 mm.